Noise-induced hearing loss and tinnitus, or ringing in the ears, can occur from exposure to loud sound. The critical factors are the noise level, measured in decibels (dB), and the duration or how long the sound is heard. As the sound level increases, the length of time that a person safely can listen to the sound decreases. A one-time exposure to an intense, "impulse" sound – like gunfire – or repeated exposures to loud sounds 85 dBA and greater – like working around machinery noise all day – has the potential to rob people of precious hearing or cause permanent ringing in the ears. 

The U.S. Bureau of Labor Statistics cites occupational hearing loss as the most commonly recorded occupational illness in manufacturing, and the second-most recorded work-related illness in the United States. Globally, the European Union, Asia and South American countries also list noise-induced hearing loss as one of the most common occupational diseases. 

While excessive noise is present in many work environments, manufacturing industries record some of the highest rates of noise induced hearing loss globally. In the United States, the manufacturing sector showed an increase in noise-induced hearing loss cases from 344 in 2011 to 488 in 2012. More than half of the cases (52 percent) were from metalworking, according to the Workplace Health and Safety Institute. A recent study by the National Institute for Occupational Safety and Health revealed that the sectors with the highest risk for developing hearing loss from noise are 1) mining, quarrying and oil and gas extraction, 2) construction and 3) agriculture, forestry, fishing and hunting. Noise-induced hearing loss is so prevalent in the mining industry that almost 27 percent of workers have been diagnosed with hearing loss.  

Employers Must Protect Workers

To protect workers from hazardous noise, employers are mandated to reduce occupational noise exposures and to provide personal protective equipment, or hearing protection devices (HPDs), when the noise cannot be lowered to acceptable limits. In the United States, HPDs must be measured in a standardized way on a small group of human subjects in an accredited laboratory. The amount of noise that is blocked is used to calculate a noise reduction rating (NRR), which must be printed on the product packaging. The NRR represents the optimal capability of the HPD when it is fit properly.

However, the typical workplace is quite different from the laboratory setting where the NRR measurements are conducted. Workers have to move around, wear other protective gear, experience changing temperatures in their environment and concentrate on getting their work done correctly. Not surprisingly, research has shown that employees typically get much less attenuation than the NRR indicates – sometimes only about one-half to one-third of the NRR. 

As a general rule, earmuffs tend to be easier to fit correctly with little training compared to earplugs. Therefore, in general, the real world attenuation from earmuffs tends to come closer to the NRR than for earplugs.